Effect of beta-carotene status in microcapsules on its in vivo bioefficacy and in vitro bioaccessibility

Highlights

• 4 kinds of high-loading beta-carotene microcapsules with different status were prepared.

• Bioefficacy was calculated as percentage using a simple animal model.

• CE microcapsules were found to be the most effective form in delivery beta-carotene in this study.

• Microcapsules with beta-carotene crystals suspended in the emulsion droplet were lower effective than expected.

• For any delivery system in this study, size was important factor influencing the micellization during digestion.

Abstract

Sufficient loading capacity and high bioefficacy are both necessary if microencapsulated beta-carotene (BC) is supplemented to overcome Vitamin A deficiency. Four high BC loading (1.2%) microcapsules (BC melted in oil, MO; BC crystals dispersed in oil, CO; BC crystals embedded in wall material, CW; and BC crystals with excipient emulsion, CE) with same wall composition were prepared and their bioefficacy (BE) were compared by in vivo and in vitro tests. BE sequence (CE > CW > MO > CO) from in vivo study was found abnormal, which indicated higher efficacy of crystal BC over melted, excipient oil over oil as solvent. Morphology, particle size and micellization rate change during in vitro GI digestion were investigated to find the reason behind the abnormal. The results suggested that BC molecule could be released from its crystal and included into bile salt micelle with the shear provided by gastric and intestinal movements, the inclusion rate is crystal size dependent; the co-exiting oil would opposite the micellization rate if the oil-BC interaction affected either the diffusion of BC or the digestion of oil. The CE microcapsule had advantages in both factors and therefore resulted in the highest in vivo hepatic VAE, although the possible existence of equilibrium hepatic VAE level (800VAE μg/g liver) led to lower relative BE at excessive BC gavage dosage with effective BC microcapsules. The results from this study challenged the conventional positive concept of encapsulating amorphous BC, provided new insight into the design of effective BC microcapsules.

Introduction

Vitamin A deficiency (VAD), mainly resulted from the low diet intake of fruit and vegetables or malabsorption of liposoluble nutrients, is becoming the main cause of acquired blindness or even high mortality of children (Harrison, 2005). Beta-carotene (BC) is one of the most effective provitamin A. But the converting rate of oral admitted BC to serum retinol is limited due to its limited solubility and low stability. Encapsulation has been widely used to improve the bio efficiency of BC, various formulas have been also compared by groups of researchers. As the solubilized amorphous state was generally considered to be crucial for in vivo absorption of BC, most of studies focused on the preparation of O/W emulsion (Han et al., 2019) microcapsules and their spray dried powders (Lin, Liang, Williams, & Zhong, 2018).

However, the low solubility of BC in various edible oils resulted in low loading capacity of those microcapsules (0.05–0.2% in oil, 0.005–0.02% in emulsion) (Liang, Shoemaker, Yang, Zhong, & Huang, 2013) and limited its application as valid VAD treatment. Therefore, microcapsules with high BC loading capacity and increasing relative physiological index such as serum response were intriguing. To achieve high BC loading, heat treatment was often adopted to increase the apparent solubility of BC crystals in core oil. Numerous studies have indicated that oil content (Yi, Lam, Yokoyama, Cheng, & Zhong, 2015), oil type (Chilungo, Muzhingi, Van-Den, & Allen, 2019), its digestion rate (Ozturk, Argin, Ozilgen, & McClements, 2015) and extent (Mutsokoti et al., 2017) were pivotal factors affecting the bioavailability of oil solubilized BC in the microcapsules. However, most of the previous reports were with low BC loading system, whether the change of BC/oil ratio in the high loading system would change the lipolysis behavior of oil and the subsequent micellization, absorption and transportation process of BC is not clear and worth investigation.

Another approach of increase BC loading capacity is through direct encapsulating BC at the form of crystalline in the wall material. Due to the fact that no oil existed in crystal BC microcapsule, it was regularly regarded as microcapsule of low bio efficiency (Xia, McClements, & Xiao, 2015). But recent reports suggested that this crystal state can also exhibited high bioavailability under certain conditions. For example, Zhang (Zhang et al., 2015) reported that the lipids free and high loading lutein crystals embedded in OSA-starch had fast solubility (85% lutein released in 15 min) and high bioavailability (high serum response) if BC crystal size is lower than 250 nm. Another interesting report is from Zou (Zou, Liu, Liu, Xiao, & McClements, 2015) who found that the bioavailability of curcumin crystals was significantly increased by the use of additional excipient emulsion (Zou et al., 2015), which suggested the contribution of uncontacted oil to the micellization of BC. However how BC molecule was detached from the crystals and micellized in the composite belt salt micelle was not discussed in the report.

In order to build microcapsules with high BC loading capacity and sufficient bioavailability, to understand the role that co-exiting oil and the BC amorphous-crystal interchange played in manipulating the in vivo performance of high BC loading microcapsules, four different structured microcapsules (BC melted in oil, MO; BC crystals dispersed in oil, CO; BC crystals embedded in wall material, CW;and BC crystals along with excipient emulsion embedded in wall material, CE) with same wall composition and BC loading were prepared and compared. Bioaccessibility and bioefficacy were determined by in vitro digestion and in vivo animal test.